The present invention relates to an exposure apparatus for use in a lithography process in a production line for manufacturing semiconductor devices, liquid crystal display devices and an exposure method using such exposure apparatus. The present invention also relates to a method for manufacturing circuit devices for use in forming electronic circuit devices on a semiconductor substrate (wafer), glass substrate, and so on.
Recently, at plants for manufacturing semiconductor devices such as super LSIs and so on, developments for mass-producing D-RAMs (memory chips), processor chips and the like, having a degree of integration and a fineness of a class of 256 Mbits on a large scale have been carried out extensively with great effort. As developments advance, exposure apparatuses for use in a next-generation lithography process (representatives being processes for coating a resist, exposing, developing resist, etc.) are also required to have a higher precision of alignment, a high resolution and a higher throughput.
At current times, at plants for manufacturing semiconductor devices, a reduced projection exposure apparatus of a step-and-repeat type has been used extensively, which uses i-rays having a wavelength of 365 nm, among emission line mainly from a mercury discharge lamp as illumination light for exposing. The projection exposure apparatus of this type is configured such that i-rays are irradiated as illumination light onto a reticle (a mask substrate) disposed on the object plane side of a projection optical system having a ⅕-fold reduction rate and a circuit pattern formed on the reticle is transcribed on a resist layer on a semiconductor wafer by means of a projection optical system. Further, the projection exposure apparatus of a step-and-repeat type is configured such that a stage with the wafer loaded thereon is transferred in a stepwise and two-dimensional manner in order to allow a sequential transcription of an image of a circuit pattern of the reticle in plural positions (shot regions) on the wafer.
Further, as a trend in these years, in order to avoid that a vision field of the projection optical system should become extremely large attendant upon enlarging a size (a chip size) of a circuit device to be formed on the wafer, a reduced projection exposure apparatus of a step-and-scan type draws attention, which step-and-scan type is to scan and expose an entire image of the circuit pattern of the reticle to the wafer by scanning the reticle in the vision field on the object plane side of the reduced projection optical system in a one-dimensional direction at an equal velocity and at the same time scanning the wafer in the vision field on the image plane side of the reduced projection optical system in a one-dimensional direction at an equal velocity.
Moreover, projection exposure apparatuses of a step-and-repeat type or of a step-and-scan type have been developed, which use ultraviolet pulse light having a wavelength of 248 nm from a KrF excimer laser light source as an exposing illumination light, and they have been begun being launched into production lines on a large scale. As such an excimer laser light source, an ArF excimer laser light source having a shorter wavelength (having a central wavelength of 193 nm) is now being developed, and it is promising in the future as an exposing light source.
In particular, in the case where such an ArF excimer laser light source is used for exposuring, it is required to narrow wavelength characteristics of pulse light to a wavelength that can avoid several absorption bands of oxygen that exist within the wavelength band in a naturally oscillating state of the pulse light. Further, it is required to replenish a majority of an illumination light path extending from the light source to the reticle and a projection light path extending from the reticle to the wafer with inert gases (such as nitrogen gas, helium gas, etc.), in order to provide an environment where oxygen is contained in the least possible amount in both of the such illumination light path and projection light path. An example of the projection exposure apparatus using such an ArF excimer laser light source is disclosed, for example, in U.S. Pat. No. 5,559,584 (Japanese Patent Application Laid-Open Nos. 6-260,385 and 6-260,386).
As an optical glass material for practical use having a desired transmittance for ultraviolet pulse light (wavelength of 250 nm or less) from the such excimer laser light source, there are currently known only two, one being quartz (SiO2) and the other being fluorite (CaF2). As a matter of course, although there are known other optical glass materials such as magnesium fluoride, lithium fluoride, and so on, they require to solve various problems with processing, durability, and so on before they are applied practically as an optical glass material for use with the projection exposure apparatus.
Moreover, in the case of use of quartz and fluorite for the projection exposure apparatus, achromatism in the projection optical system becomes difficult upon using illumination light. Therefore, a narrow-banded laser light source is preferred from the point of view of easiness of performing achromatism in the projection optical system.
It should be noted herein, however, that a band of such an excimer laser light is originally a broad band, so that a narrow-banded laser light source has its oscillating spectrum narrowed by injection locking, etc. From these reasons, the narrow-banded laser light source suffers from the disadvantages that a laser output is lowered as compared with a broad-band laser light source, and its life is shorter and its costs of production is more expensive than the broad-band laser light source. Therefore, the broad-banded laser light source is more favored in terms of the laser output, life and costs of production than the narrow-banded laser light source. Recently, attempts have been made to use a broad-banded laser light source for a projection optical system having a structure in which achromatism can be done easily.
There are known several types of projection optical systems to be mounted on the projection exposure apparatus. Among them, the types of the projection optical systems for exposure apparatuses which are used for large-scale commercial production lines can be divided into two major types, one being a dioptric type that is composed of a plurality of refractive optical elements (lens elements) only and the other being a catadioptric type that is composed of a combination of such refractive optical elements with reflective optical elements (particularly a concave mirror).
In the case of using a reflection-refraction optical system as of a catadioptric type, the concave mirror is free from chromatic aberration, so that achromatism can be effected easily by locating the concave mirror in a group of refractive lenses. As a result, a broad-banded laser light source can be used which is advantageous in terms of the laser output, life, etc. On the other hand, in the case of using a refractive optical system only as of a dioptric type, too, a broad-banded laser light source can be used because a range of achromatism can be widened by making a rate of fluorite contained in the entire refractive lenses larger.
In a current situation, however, even which type of the projection optical system is adopted, the refractive optical elements (light-transmitting optical elements) have to be used. Therefore, at this point of time, there is no way but using two kinds of glass materials, i.e. quartz and fluorite, for the refractive optical elements. Further, each of the refractive optical elements and the reflective optical elements is produced so as to achieve a desired performance as a single optical element by forming a multi-layer membrane such as a reflection preventive layer, a protective layer, etc. by deposition etc. on a surface of each element. The performance to which attention should be paid herein is how large an absolute value of transmittance or transmissivity of the single lens element or an absolute value of reflectance or reflectivity of the single reflective optical element can be set.
For instance, in the case of the single lens element, it is arranged so as to make transmittance as high as possible by coating a reflection preventive layer, etc. on both surfaces of the element, i.e. the incident surface to which the light is entered and the leaving surface from which the light leaves. In a high-precision imaging optical element of this kind, as much as 20-30 sheets of lens elements are to be used for achieving a high correction of various aberration characteristics. In such a case, a transmittance of the entire projection optical elements is reduced to a large extent even if a slight reduction in transmittance would occur in each lens element. In addition, it is required to make a reflectance of each reflective element larger even for the projection optical system containing a large number of reflective optical elements in a similar manner.
For instance, suppose that an imaging light path of the projection optical system is composed of 25 sheets of the lens elements and the transmittance is set to be 96% for each lens element, the transmittance e for the entire projection optical system becomes approximately 36% (0.96 to the 25th power). If it is assumed that a transmittance of each single lens element would be decreased by 1%, the transmittance e of the entire projection optical system is reduced to approximately 27.7% (0.95 to the 25th power).
In the case where the transmittance of the projection optical system is low, this can be improved by increasing the intensity (energy) of illumination light for exposing a circuit pattern image of a reticle onto a semiconductor wafer (a photosensitive substrate) and developing a photoresist for ultraviolet rays having a higher degree of photosensitivity. If such improvements could not be made, a throughput will be decreased due to an increase in a longer period of time for exposure. A decrease in throughput is unacceptable, because it results in higher costs for the production of devices. Therefore, it may be a one of possible solution to prepare an excimer laser light source having a higher output.
As a result of experiments for various exposure by a projection exposure apparatus having a relatively large field size using an excimer laser light source, however, a new phenomenon has been discovered in that a transmittance of an optical element or a coating material (for example, a thin membrane, such as a reflection preventive membrane, etc.) for the optical element in the projection optical system fluctuates in a dynamic mode by irradiation of illumination light of an ultraviolet wavelength region (a KrF excimer laser having a wavelength of 248 nm, an ArF excimer laser having a wavelength of 193 nm, etc.). This phenomenon has been found to occur for an optical element in an illumination optical system for illuminating a reticle and a reticle (a quartz plate) itself, too, in the same manner as described above, as well as for the optical element in the projection optical system.
It is considered that such phenomenon is caused by, for instance, attachment or penetration (floating) of impurities contained in gases (air, nitrogen gas, etc.) present in a space within the projection light path or the illumination light path, gaseous molecules of organic substances to be caused to generate from adhesive or the like to be used for fixing the optical element to the barrel, or impurities (for example, water molecules, hydrocarbon molecules or other substances for dispersing the illumination light) to be caused to generate from the inner wall of the barrel (for example, a coated wall surface for prevention of reflection, etc.) to the surface of the optical element or in the illumination light path.
As a consequence, severe problems may occur that the transmittance of the projection optical system or the transmittance of the illumination optical system may fluctuate to a great extent for a relatively short period of time. Such a great fluctuation of the transmittance results in a decrease in a precision for controlling the exposure amount to be provided on the photosensitive substrate, thereby deteriorating a fidelity of transcription of a fine pattern having a design line width of 0.25 to 0.12 micron to be transcribed on the substrate.
The projection exposure apparatus of a conventional type as disclosed, for example, in Japanese Patent Application Laid-Open No. 2-135,723 (U.S. Pat. No. 5,191,374) is configured such that the optical intensity of illumination light is detected at an appropriate portion in a light path in the illumination optical system and the intensity (energy per one pulse) of the pulse light from an excimer laser light source is adjusted so as to achieve an optimal exposure amount on the basis of the detected optical intensity. Therefore, the such conventional projection exposure apparatus suffers from the disadvantage in that no accurate control of the exposure amount can be performed because no fluctuation in the transmittance of the illumination optical system and the projection optical system behind the portion in the illumination light path is added thereto whatsoever, the portion in the illumination light path being the place where the intensity of the illumination light has been detected for controlling the exposure amount.
In addition, for the causes as described above, there is no assurance that the fluctuation in the transmittance of the projection optical system and the illumination optical system occurs in a uniform manner in the vision field on the image plane side of the projection optical system, so that there is the risk that irregularities of illuminance (or irregularities of the exposure amount) will occur against the projection optical system within the projection region of the pattern image conjugated with the illumination region of the illumination light on the reticle. Furthermore, there is the concern about an occurrence of the disadvantage that imaging characteristics (e.g., distortion, spherical aberration, astigmatism, coma aberration, etc.) of the projection optical system may vary to a subtle extent, attendant upon an occurrence of such irregularities of illuminance or otherwise.
Therefore, the present invention has the object to provide an exposure apparatus that can reduce deterioration in precision for controlling the exposure amount resulting from a fluctuation of illuminance or irregularities of illuminance on a photosensitive substrate or on a mask (reticle) which may occur due to a variation in transmittance or transmissivity of the projection optical system or the illumination optical system. The present invention has another object to provide an exposure apparatus can detect a variation in transmittance of the projection optical system or the illumination optical system at a semi-real time, even during a period of time of operations of exposure to the photosensitive substrate.
In another aspect, the present invention has a further object to provide an improved measurement method for measuring a transmittance in an image projection region of the projection optical system or measuring an average illuminance or an irregularity of illuminance in the image projection region of the projection optical system. In a further aspect, the present invention has a still further object to provide a method for manufacturing a circuit device that can form a pattern image of a circuit device on the substrate always at an appropriate amount of exposing light and in a favorable imaging state.
In a still further aspect, the present invention has an object to provide an exposure apparatus of a scanning type and an exposure method using the same, which can always provide the photosensitive substrate with an appropriate amount of exposing light, even if transmittance of the projection light path or the illumination light path would fluctuate during scanning the mask (reticle) and the photosensitive substrate in synchronism with the projection optical system.
A first mode of the present invention can be applied to an exposure apparatus comprising an irradiation means (a laser light source, a condenser lens system, etc.) for irradiating a pattern formed on a mask (reticle) with an exposing energy (excimer laser, fluorine laser, SOR rays having a wavelength of 50 nm or less, etc.) and a projection optical system for projecting an image of the pattern on the mask at a given position on a photosensitive substrate (wafer). The exposure apparatus is characterized by a reflecting member disposed in a Fourier transform plane or in at least a part of a plane in the vicinity thereof between an object plane and an image plane of the projection optical system, and which reflects the exposing energy incident from the object plane side of the projection optical system or an exposing energy incident from the image plane side of the projection optical system; a beam irradiation means which irradiates the exposing energy as measuring beams in a nearly collimated state from the object plane side or the image plane side of the projection optical system toward the reflecting member; a detection means which detects the energy reflected by the reflecting member and outputs a detection signal in accordance with the reflected energy; and an exposure control means (a processor, a light source control system, a main control system, etc.) which sets an exposing condition for the photosensitive substrate based on the detection signal from the detection means in order to reduce deterioration in a control precision for an amount of exposing light resulting from a variation in an attenuation factor (a variation in transmittance or in reflectance) of the projection optical system.
In another mode, the present invention is applied to a method for scanning-exposing an entire image of the pattern of a mask or reticle (R) on a substrate (wafer) to be exposed, which is carried by scanning the mask (reticle) and the substrate relative to the vision field of the projection optical system, while irradiating a portion of the pattern of the mask (reticle) with an exposing energy (ultraviolet laser light, etc.) having a wavelength of 250 nm or less and projecting a partial image of the pattern onto the substrate (a wafer) through a projection optical system. The method is characterized by the steps of; irradiating the exposing energy onto the reflecting member disposed in a Fourier transform plane formed between the object plane and the image plane of the projection optical system or at least at a portion in a plane in the vicinity of the Fourier transform plane prior to starting scanning exposure, and then detecting the intensity of an energy reflected from the reflecting member; and setting an exposing condition (updating database at step 328) for transcribing the entire image of the pattern of the mask on the substrate at a predetermined exposure amount in accordance with the intensity detected.
Further, the present invention is applied to a manufacturing method for forming a circuit device on the substrate by practicing a lithography process in which the circuit pattern of the mask (reticle) is irradiated with an exposing energy having a wavelength of 250 nm or less and then exposing the circuit pattern to each of plural positions on the substrate (wafer) one after another through the projection optical system while projecting the exposing energy. The method is characterized by the steps of; detecting the intensity of the exposing energy passing through a projection light path, including a portion of a variation by a transmittance of the projection optical system, through a reflecting member disposed in a Fourier transform plane formed in the projection light path of the projection optical system or at least at a portion in a plane in the vicinity of the Fourier transform plane; and setting an exposing condition (updating database at step 328) for exposing the substrate at a target exposure amount in order to reduce deterioration in precision for controlling the exposure amount resulting from a variation in an attenuation factor (a variation in transmittance or a variation in reflectance) of the projection optical system in accordance with the energy intensity detected.
In the first mode of the present invention, the exposure can be controlled so as to provide the photosensitive substrate always with an optimal exposure amount with a variation added thereto, even if the transmittance of the refractive (light-passing) optical elements constituting the irradiation system and the projection optical system would vary with time during the exposure operation.
Moreover, the present invention is configured such that the exposing energy reflected at the Fourier transform plane (pupil plane) of the projection optical system for projecting the pattern of the mask onto the photosensitive substrate can be detected in a photoelectric mode, so that, upon exposing a plurality of shot regions on the photosensitive substrate one after another, a portion of the exposing energy (monitoring beams for measuring) which underwent a variation in an attenuation factor (a variation in transmittance or a variation in reflectance) can be detected in a photoelectric mode in a short time during subsequent exposure of the shot regions.
The variation in the attenuation factor (the variation in transmittance or in reflectance) of the illumination optical system and the projection optical system can appear in a remarkable way, in particular when an ultraviolet light having a wavelength of 200 nm or less is used. It is also known that an ArF excimer laser light source, F2 (fluorine) laser light source, etc. can be included in that category of the light. Therefore, in a projection exposure apparatus using such a laser light source, an error in controlling the exposure amount may occur due to a variation in the transmittance of the illumination optical system and the projection optical system. In the present invention, however, the reflecting member is disposed at a portion of the Fourier transform plane of the projection optical system, and a portion of the exposing energy passed through the projection optical system is allowed to be detected in a photoelectric mode at a nearly real time, thereby enabling reduction of an error due to the variation in the transmittance upon controlling the exposure amount.
One of the causes of an occurrence of a variation in the attenuation factor (a variation in transmittance or in reflectance) in the ultraviolet region below a wavelength of 200 nm or less is because of the physical properties of an optical glass material itself. Another cause is considered to be due to molecules of impurities to be attached to (or deposited on) such an optical glass material. Among those causes, in particular, the molecules of the impurities to be attached to the surface of the optical glass material may cause a decrease in an attenuation factor (transmittance or reflectance) in a monotonous way, if they are left non-removed and stayed as they are. However, once the exposing energy is irradiated, they would be caused to be decomposed chemically and to disperse in a space. As a consequence, the attenuation factor (transmittance or reflectance) is allowed to rise to its original value.
This means to cause the entire attenuation factor (transmittance or reflectance) of the projection optical system and the illumination optical system to fluctuate, each being incorporated with a number of optical elements, and it is difficult to monitor a history of irradiation and the like and to predict characteristics of a variation in the attenuation factor (transmittance or reflectance). In accordance with the present invention, however, the variation in transmittance can be detected in an accurate way without effecting complicated computation processing for conducting such a prediction. Therefore, the control of the exposure amount can be conducted in a precise manner on the basis of the detection.
Moreover, the exposing energy reaching the Fourier transform plane of the projection optical system from the illumination optical system through the projection optical system can be detected, so that the variation in the attenuation factor (the variation in transmittance or the variation in reflectance) of the entire system including both of the illumination optical system and the projection optical system can be detected in an accurate mode, thereby enabling the accurate control of the exposure amount.
A second mode of the present invention can be applied to a projection exposure apparatus comprising the irradiation means for irradiating the pattern formed on the mask (reticle) with the exposing energy (pulse light from the excimer laser light source) having a wavelength in an ultraviolet range; and the projection optical system for projecting an image of the pattern of the mask to a predetermined positions on the photosensitive substrate (wafer). The projection exposure apparatus is characterized by a first detection means which is disposed in the vision field of the projection optical system outside the image projection region (illumination region) on which the image of the pattern of the mask is projected, and which receives at least a portion of the exposing energy (a monitoring light) directed to the side of the photosensitive substrate through the projection optical system and outputs a detection signal in accordance with the intensity thereof; a second detection means which detects the intensity of the exposing energy in the predetermined positions in a light path extending from the light source disposed in the irradiation means and outputs detection signal in accordance with the intensity thereof; a variation detection means (a control processor) which detects a variation in an attenuation factor (transmittance or reflectance) for the exposing energy on the basis of the detection signal from each of the first detection means and the second detection means, the variation occurring at a light path in the irradiation means or at a light path in the projection optical system (PL); and an exposure control means (an exposure control unit containing a processor) which corrects an exposing condition so as to provide the photosensitive substrate with a desired exposure amount, when the variation in the attenuation factor (transmittance or reflectance) is detected by the variation detection means.
Further, a second mode of the present invention can be applied to a projection exposure apparatus for subjecting an entire image of the pattern of the mask on a photosensitive substrate by exposing and scanning them relative to each other, which is comprised of the irradiation means for irradiating the exposing energy (e.g., pulse light from the excimer laser light source) having a wavelength in an ultraviolet region, the projection optical system for projecting a partial image of the pattern onto the photosensitive substrate (wafer) by irradiating a portion of the pattern formed on the mask (reticle) with the exposing energy from the irradiation means, and the scanning mechanism (a stage, a drive control unit) for scanning the mask and the photosensitive substrate relative to the vision field of the projection optical system. The projection exposure apparatus is characterized by a restriction means (a reticle blind mechanism) which restricts an image pattern region (within an illumination region) where a partial image of the pattern of the mask is projected to a polygonal or arc-shaped region extending in a direction intersecting with a relative scanning direction in the vision field of the projection optical system; a detection means which is disposed in the vision field of the projection optical system and in a region outside the image projection region (illumination region) relating to the relatively scanning direction and which receives at least a portion of the exposing energy (a monitoring light) directed to the photosensitive substrate side through the projection optical system and outputs a detection signal in accordance with the intensity thereof; and an exposure control means (a main control system, an exposure control unit) which sets an exposing condition (an intensity of illumination light, a scanning velocity, an opening width of a blind, etc.) and controls the scanning exposure in accordance with the exposing condition.
The present invention further provides the exposing and scanning method which is characterized by the steps of: restricting the image projection region (defined by the illumination region) on which a partial image of the pattern is projected, upon scanning exposure, to a polygonal or arc-shaped region (set by the reticle blind mechanism) extending in a direction intersecting with the relative scanning direction within the vision field of the projection optical system; detecting the intensity of at least a portion of the exposing energy passing through a region outside the image projection region (corresponding to the illumination region) relating to the relative scanning direction in the vision field of the projection optical system prior to the start of the scanning exposure; and setting the exposing condition (the intensity of the illumination light, the scanning velocity, the opening width of the blind, etc.) for transcribing an entire image of the pattern on the substrate to be exposed at a desired exposure amount (an operation by the exposure control unit) prior to the start of the scanning exposure on the basis of the detected intensity thereof.
Furthermore, another mode of the present invention is applied to a manufacturing method for forming the circuit device on the substrate by practicing the lithography process involving projection exposing the circuit pattern formed on the mask (reticle) to each of plural positions (shot regions) on the substrate (wafer) one after another through the projection optical system by irradiating the circuit pattern with the exposing energy (for example, ultraviolet pulse laser) of an ultraviolet region having a wavelength of 250 nm or less; in which an deterioration in a precision of controlling the exposure amount by a variation in the attenuation factor (a variation in transmittance or a variation in reflectance) of the projection optical system, which may occur during projection exposing the image of the circuit pattern on the substrate one after another, can be reduced by carrying out the step for detecting a variation in the intensity of the exposing energy resulting from the variation in the attenuation factor (the variation in transmittance or the variation in reflectance) of the projection optical system, by detecting at least a portion of the exposing energy (a monitoring light) travelling toward the substrate side through an outer region of the image projection region (defined by the illumination region) in which the image of the circuit pattern of the mask to be formed within the vision field of the projection optical system, and the step (the operation processing by the exposure control unit) for setting the exposing condition (an intensity of illumination light, a scanning velocity, an opening width of a blind, etc.) for transcribing the circuit pattern onto the substrate at a given exposure amount on the basis of the variation in the detected intensity thereof.
In the second embodiment of the present invention, even if the attenuation factor (transmittance or reflectance) of a number of the light-transmitting optical elements and reflecting optical elements constituting the illumination system and the projection optical system would fluctuate during the exposing operation, the exposure can be controlled so as to provide the photosensitive substrate always with an optimal exposure amount, with the such fluctuation added thereto. Further, in this embodiment, the exposing energy can be detected in a photoelectric mode outside the image projection region on which the pattern of the mask is to be projected. With this configuration, the present invention can potoelectrically detect the portion of the exposing energy (the monitoring light) which is subjected influences from the variation of the attenuation factor (variation in transmittance or variation in reflectance) during a short period of time during which the plural shot regions on the photosensitive substrate are being exposed one after another.
It is known that the variation in the attenuation factor (variation in transmittance or variation in reflectance) of the illumination system and the projection optical system occurs to a remarkable extent, particularly when ultraviolet light having a wavelength of 200 nm or less is used, and that an ArF excimer laser light source is one of such light sources having such a wavelength region. Therefore, a conventional projection exposure apparatus using such an ArF laser light source has an error which may occur in controlling the exposure amount due to a variation in the attenuation factor (variation in transmittance or variation in reflectance) of the illumination system and the projection optical system. In the embodiment of the present invention, however, it is modified so as to reduce an error that may be caused by such a variation in the attenuation factor (variation in transmittance or variation in reflectance) by photoelectrically detecting the exposing energy passed through the projection optical system at a nearly real time.
With those configuration, like the first embodiment as described above, the second embodiment of the present invention can detect the variation in the attenuation factor (variation in transmittance or variation in reflectance) in a precise mode and perform an accurate control of the exposure amount even without conducting a complex prediction computation.
In the third embodiment of the present invention, the projection exposure apparatus for transcribing a transcribing pattern on a mask onto a photosensitive substrate by irradiating the transcribing pattern with an illumination light in an ultraviolet wavelength region and projecting the transcribing pattern onto the photosensitive substrate through the projection optical system, which is characterized by a sensing means for sensing a variation in an attenuation factor (variation in transmittance or variation in reflectance) of the projection optical system, which depends upon irradiation of the illumination light of an ultraviolet wavelength region, and by a control unit that can maintain an illuminance of the illumination light on the photosensitive substrate at a nearly constant level during exposure on the basis of an output from the sensor.
In this embodiment, a sensor (604A) for sensing the variation in the attenuation factor (variation in transmittance or variation in reflectance) of the projection optical system as the sensing means is disposed, so that an occurrence of a variation in illuminance or irregularity of illuminance on the photosensitive substrate due to the variation in the transmittance can be prevented.
Further, such a sensor for sensing the variation in the attenuation factor (variation in transmittance or variation in reflectance) is preferably configured such that it can receive a portion of light reflected from the photosensitive substrate. The sensor of such a type can sense a variation in illuminance of the illumination light on the photosensitive substrate during exposure.
Moreover, it is preferred to provide a light receipt element for receiving a portion of the illumination light having an ultraviolet wavelength region incident to the mask, and to use an output from each of the light receipt element and the sensor (604A) for the control unit. This configuration can correct an error in the exposure amount on the photosensitive substrate which may occur due to the variation in the attenuation factor (variation in transmittance or variation in reflectance) as described above, based on the output of the sensor (604A), upon controlling the accumulated light quantity on the photosensitive substrate to an optimal dose amount on the basis of the output from the light receipt element.
Moreover, in this embodiment of the present invention, it is desired to measure an average illuminance (i.e., an accumulated exposure amount) at least in the exposure region of the projection optical system or an irregularity of illuminance values in the exposure region of the projection optical system as an illuminance of the illumination light on the photosensitive substrate. This allows an appropriate control of the exposure amount in the exposure region on the projection optical system to an optimal value.
In another mode of this embodiment of the present invention, the projection exposure apparatus for transcribing a transcribing pattern on a mask onto a photosensitive substrate by irradiating the transcribing pattern on the mask with the illumination light of the ultraviolet wavelength region, and for projecting the transcribing pattern onto the photosensitive substrate through the projection optical system, which is characterized by a sensor (604A) for sensing a variation in an imaging characteristic (for example, a magnification of projection, a focal position and at least one of five aberrations of Seidel) of the projection optical system on the basis of the variation in the attenuation factor (variation in transmittance or variation in reflectance) of the projection optical system, which depends upon the irradiation of the illumination light of the ultraviolet wavelength region, and by a control unit for controlling the imaging characteristic of the projection optical system on the basis of an output from the sensor.
With the configuration of the sensor (604A) for sensing the variation in the imaging characteristics of the projection optical system in the manner as described above, the present invention can prevent a variation in the imaging characteristics of the projection optical system to be caused due to the variation in the attenuation factor (variation in transmittance or variation in reflectance) as described above.
In a further mode of this embodiment of the present invention, the projection exposure apparatus for transcribing a transcribing pattern on a mask sequentially onto a photosensitive substrate by irradiating the transcribing pattern with the illumination light of an ultraviolet wavelength region and by transferring the mask and the photosensitive substrate in synchronization with the projection optical system, which is characterized by an adjustment device for adjusting at least one of an intensity of the illumination light on the photosensitive substrate, a scanning velocity for scanning the photosensitive substrate, and a width of the illumination region of the illumination light involved in the scanning direction of the photosensitive substrate, on the basis of the variation in the attenuation factor (variation in transmittance or variation in reflectance) of the projection optical system depending upon the irradiation of the illumination light of the ultraviolet wavelength region.
With the configuration as described above, the present invention can always provide the photosensitive substrate with an optimal exposure amount even if the attenuation factor (variation in transmittance or variation in reflectance) of the projection optical system would fluctuate during the movement of the mask and the photosensitive substrate in synchronism with each other.
In this embodiment of the present invention, when the illumination light of the ultraviolet wavelength region is pulse light, it is preferred to adjust at least one of a frequency of oscillation of the pulse light, the intensity of the illumination light, the scanning velocity for scanning the photosensitive substrate, and the width of the illumination region.
In another embodiment of the present invention, the method for the production of micro devices (for example, semiconductor elements, image pickup elements (CCDs, etc.), liquid crystal display elements, or thin film magnetic heads) is carried out by a method for the production of the micro devices, including a photolithography process in which a device pattern is irradiated with an illumination light of an ultraviolet wavelength region and an image of the device pattern to be projected by the projection optical system is exposed to a substrate, which is characterized by detecting an illuminance of the illumination light on the substrate, and an irregularity of illuminance and an image characteristic of the device pattern (for example, a magnification, focal position and at least one of the five aberrations of Seidel) on the basis of the variation in the attenuation factor (variation in transmittance or variation in reflectance) of the projection optical system which may be caused by the irradiation of the illumination light of the ultraviolet wavelength region during exposure.
With the configurations as described above, the present invention can expose the image of the device pattern to the substrate always at an optimal exposure amount and in a good imaging state, thereby enabling the production of the micro devices without reducing a yield rate of production, even if the transmittance of the projection optical system would vary.